A disk drive system is a digital data storage device that stores information within tracks on a storage disk. The storage disk may, for example, include a magnetic, an optical, or a magneto-optical material that is capable of storing data. During operation of the disk drive, the disk is rotated about a central axis. To read data from or write data to the disk, a magnetic transducer is positioned above a desired track of the disk while the disk is spinning.
A conventional magnetic disk drive, generally designated 10, is illustrated in FIG. 1. The disk drive comprises a storage disk 12 that is rotated by a spin motor 14. The spin motor 14 is mounted to a base plate 16. An actuator arm assembly 18 is also mounted to the base plate 16.
The actuator arm assembly 18 includes a transducer 20 mounted to an actuator arm 22 that can rotate about a bearing assembly 26. The actuator arm assembly 18 includes a voice coil motor (VCM) 28, which moves the transducer 20 relative to the disk 12. The spin motor 14, VCM 28 and transducer 20 are coupled to a number of electronic circuits 30 mounted to a printed circuit board 32. The electronic circuits 30 typically include one or more read channel chips, a microprocessor-based controller and a random access memory (RAM), among other things.
Instead of having a single disk 12 as shown in FIG. 1, as is well-known in the art, the disk drive 10 may include a plurality of disks 12. In such case, each of the plurality of disks 12 may have two sides, with magnetic material on each of those sides. Therefore, two actuator arm assemblies 18 may be provided for each disk 12.
Referring now to FIG. 2, data is stored on the disk 12 within a number of concentric radial tracks 40 (or cylinders). Each track is divided into a plurality of sectors 42. Each sector 42 is further divided into a servo region 44 and a data region 46.
The servo regions 44 of the disk 12 are used to, among other things, accurately position the transducer 20 so that data can be properly written onto and read from the disk 12. The data regions 46 are where non-servo related data (i.e., user data) is stored and retrieved. Such data, upon proper conditions, may be overwritten.
FIG. 3 shows portions of tracks 40 for a disk 12 drawn in a straight, rather than arcuate, fashion for ease of depiction. To accurately write data to and read data from the data region 46 of the disk 12 (see FIG. 2), it is desirable to maintain the transducer 20 in a relatively fixed position with respect to a given track's centerline 48 during each of the writing and reading procedures. Tracks n−2 through n+1, including their corresponding centerlines 48, are shown in FIG. 3.
To assist in controlling the position of the transducer 20 relative to the track centerline 48, the servo region 44 contains, among other things, servo information in the form of servo patterns 50 comprised of one or more groups of servo bursts, as is well-known in the art. First, second, third and fourth servo bursts 52, 54, 56, 58 (commonly referred to as A, B, C and D servo bursts, respectively) are shown in FIG. 3. The servo bursts 52, 54, 56, 58 are accurately positioned relative to the centerline 48 of each track 40. Unlike information in the data region 46, servo bursts 52, 54, 56, 58 may not be overwritten or erased during normal operation of the disk drive 10.
As the transducer 20 is positioned over a track 40 (i.e., during a track following procedure), it reads the servo information contained in the servo regions 44 of the track 40, one servo region 44 at a time. The servo information is used to, among other things, generate a position error signal (PES) as a function of the misalignment between the transducer 12 and a desired position relative to the track centerline 48. As is well-known in the art, the PES signals are input to a servo control loop (not shown) which performs calculations and outputs a servo compensation signal which controls the VCM 28 to, ideally, place the transducer 12 at the desired position relative to the track centerline 48.
A servo track writer (STW) is used to write servo regions 44, including their corresponding fields, onto the surface(s) of the disk 12 during the manufacturing process. The STW controls the transducers 20 corresponding to each disk surface of the disk drive system 10 to write the servo regions 44. In order to precisely write the servo regions 44 at desired locations on the disk 12, the STW directs each transducer 20 to write in small steps, with each step having a width (i.e., STW step width 72 as shown in FIG. 3).
FIG. 3 illustrates the relationship between the STW step width 72 and the pitch 74 of the servo region 44 for a conventional disk drive system. For convenience, the tracks 40 are shown as being straight, rather than arcuate, for ease of depiction.
As used herein, the term “pitch” is the radial distance between centers of adjacent regions on the surface of a disk 12. For example, a servo track pitch 74 (shown in the data region 46 of FIG. 3) is the distance between the centers of radially adjacent servo regions 44. In contrast, the term “width” is defined as the radial distance from one end to the other end of a single region. For example, a servo track width 75 (shown in the data region 46 of FIG. 3) is the width from one end to another of a single servo region 44.
For each servo region 44, the servo track pitch 74 is generally equivalent to the servo track width 75. However, for data regions 46, the data track pitch 76 is generally different from the actual data track width (not shown) due to, for example, the presence of erase bands which are typically found on both sides of each data region 46. For simplicity, the effects that reduce the data track width are not shown in the figures. Instead, the data track width is shown to be the same as the data track pitch.
A STW can include a table that defines a servo track pitch for writing the servo regions on a disk. The table can include, for example, a nominal servo track pitch and a reduced servo track pitch. The STW may test whether it can write and then read information from a predetermined radial location that is near a peripheral portion on the disk. If the written information is successfully read, the STW then writes servo regions on the disk with the nominal servo track pitch. However, if the written information is not successfully read, then the STW writes the servo regions on the disk with the reduced servo track pitch.